Even though the automotive industry has over the years, if for no other reason than seeking competitive advantages, continually exerted efforts to increase the fuel economy of automotive engines, the gains continually realized thereby have been deemed by various levels of governing or regulatory bodies as being insufficient. Further, such levels of governing or regulatory bodies have also arbitrarily imposed regulations specifying the maximum permissible amounts of carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NO.sub.x) which may be emitted by the engine exhaust gases into the atmosphere.
Unfortunately, generally, the available technology employable in attempting to attain increases in engine fuel economy is contrary to that technology employable in attempting to meet legally imposed standards on exhaust emissions.
For example, the prior art in trying to meet the standards for NO.sub.x emissions has employed a system of exhaust gas recirculation whereby at least a portion of the exhaust gas is reintroduced into the cylinder combustion chamber to thereby lower the combustion temperature therein and consequently reduce the formation of NO.sub.x.
The prior art has also proposed the use of engine crankcase recirculation means whereby the vapors which might otherwise become vented to the atmosphere are introduced into the engine combustion chambers for further burning.
The prior art has also proposed the use of fuel metering means which are effective for metering a relatively overly rich (in terms of fuel) fuel-air mixture to the engine combustion chamber means as to thereby reduce the creation of NO.sub.x within the combustion chamber. The use of such overly rich fuel-air mixtures results in a substantial increase in CO and HC in the engine exhaust which, in turn, requires the supplying of additional oxygen, as by an associated air pump, to such engine exhaust in order to complete the oxidation of the CO and HC prior to its delivery into the atmosphere.
The prior art has also heretofore proposed employing the retarding of the engine ignition timing as a further means for reducing the creation of NO.sub.x. Also, lower engine compression ratios have been employed in order to lower the resulting combustion temperature within the engine combustion chamber and thereby reduce the creation of NO.sub.x.
The prior art has also proposed the use of various forms of fuel metering injection means for eliminating the usually employed carbureting apparatus and, under superatmospheric pressure, injecting the fuel through individual nozzles directly into the respective cylinders of a piston type internal combustion engine. Such fuel injection systems, besides being costly, have not proven to be generally successful in that the system is required to provide metered fuel flow over a very wide range of metered fuel flows. Generally, those prior art injection systems which are very accurate at one end of the required range of metered fuel flows, are relatively inaccurate at the opposite end of that same range of metered fuel flows. Also, those prior art injection systems which are made to be accurate in the mid-portion of the required range of metered fuel flows are usually relatively inaccurate at both ends of that same range. The use of feedback means for altering the metering characteristics of such prior art fuel injection systems has not solved the problem of inaccurate metering because the problem usually is intertwined within such factors as: effective aperture area of the injector nozzle; comparative movement required by the associated nozzle pintle or valving member; inertia of the nozzle valving member; and nozzle "cracking" pressure (that being the pressure at which the nozzle opens). As should be apparent, the smaller the rate of metered fuel flow desired, the greater becomes the influence of such factors thereon.
It is anticipated that the said governing bodies will be establishing even more stringent exhaust emission limits and engine fuel economy requirements.
The prior art, in view of such anticipated requirements with respect to NO.sub.x, has suggested the employment of a "three-way" catalyst, in a single bed, within the stream of exhaust gases as a means of attaining such anticipated exhaust emission limits. Generally, a "three-way" catalyst is a single catalyst, or catalyst mixture, which catalyzes the oxidation of hydrocarbons and carbon monoxide and also the reduction of oxides of nitrogen. It has been discovered that a difficulty with such a "three-way" catalyst system is that if the fuel metering is too rich (in terms of fuel), the NO.sub.x will be reduced effectively but the oxidation of CO will be incomplete; if the fuel metering is too lean, the CO will be effectively oxidized but the reduction of NO.sub.x will be incomplete. Obviously, in order to make such a "three-way" catalyst system operative, it is necessary to have very accurate control over the fuel metering function of associated fuel metering supply means feeding the engine. As hereinbefore described, the prior art has suggested the use of fuel injection means, employing respective nozzles for each engine combustion chamber, with associated feedback means (responsive to selected indicia of engine operating conditions and parameters) intended to continuously alter or modify the metering characteristics of the fuel injection means. However, as also hereinbefore indicated, such fuel injection systems have not proven to be successful.
It has also heretofore been proposed to employ fuel metering means, of a carbureting type, with feedback means responsive to the presence of selected constituents comprising the engine exhaust gases. Such feedback means were employed to modify the action of a main metering rod of a main fuel metering system of a carburetor. However, tests and experience have indicated that such a prior art carburetor and such a related feedbackk means apparently will never provide the degree of accuracy required in the metering of fuel to an associated engine as to assure meeting, for example, the said anticipated exhaust emission standards.
The prior art has also proposed the use of an injection system wherein a sonic nozzle-like member or flow restrictor is employed in order to accelerate a stream of air and metered fuel in order to cause atomization of the fuel prior to discharge thereof into the engine induction system. One such prior art system is shown by U.S. Pat. No. 4,292,945 dated Oct. 6, 1981. That is, in said U.S. Pat. No. 4,292,945, conduit means 88 supplies all of the air needed to sustain idle engine operation when the throttle valve means 16 is closed. As can be seen a flow circuit is described by inlet 90 of conduit 88, conduit 88, passage means 70, passage means 82, annulus 100, orifice means 102 and engine intake manifold induction passage means 13; such provides all of the air flow to the engine 20 required for idle engine operation. The restriction means 78 is of a size as to result in the flow through passage 82 being sonic during idle engine operation. The fuel which is metered by valve member 74 and injected into passage 70 mixes with the air as the metered fuel and air flow into inlet 84 of venturi nozzle-like means 78 and become accelerated to sonic velocity. The fuel within such fuel-air mixtures becomes atomized as it undergoes acceleration to sonic velocity and subsequent expansion in portion 86 of venturi means 78. The atomized fuel-air mixture then is discharged through the discharge port means 102 into passage means 13 of engine 20.
One of the problems discovered with a system as that described by said U.S. Pat. No. 4,292,945 is that of sizing of the sonic venturi (said means 78). That is, when the said sonic venturi is sized to provide just enough air flow for the low speed engine idle condition, the venturi size becomes, at best, marginal in its ability to pass the maximum fuel flow that is required and occurs at a wide open throttle high engine speed condition. If the said venturi is sized to flow the required maximum fuel flow, it then flows an excessive amount of air at the low speed engine idle condition.
The invention as herein disclosed, described and claimed is primarily directed to the solution of the aforestated and other related and attendant problems especially as they relate to the structure and teachings of said U.S. Pat. No. 4,292,945.